This invention relates to an improvement in a shaft-sealing sliding member.
In general cases of sliding portions for shaft sealing, the sealed fluids are utilized as lubricants. Since sliding portions have to prevent the sealed fluid from leakage, the sealing surfaces are subjected to boundary friction or almost solid friction. Accordingly, various severe conditions are required of the sliding members, that is, they have to be excellent in self-lubricating property, wear resistance and strength.
Especially in the shaft-sealing sliding members used for the compressors of car air conditioners, it is hardly allowed to leak the sealed fluids through sealing surfaces. In addition, since the car air conditioners are made light in weight and small in size, the sliding conditions become severer owing to the decrease of lubricant quantity contained in the sealed fluid, the raise of rotational speed and the thermal influences given by car engines.
More particularly, in the compressors of car air conditioners, seat rings are generally fixed to the casings of compressors and follower rings as the shaft-sealing sliding members are disposed opposite to the seat rings in the casings, and further, gaskets are stuffed between the follower rings and the driving shafts of compressors which pass through the axis of each ring, thereby attaining the sealing action. The above-mentioned follower rings are pressed toward the seat rings by the force of springs. Accordingly, the follower rings are brought into close contact with the seat rings and rotated together with drive shafts. The refrigerant gas is thus prevented from leakage to the outer air by the above contact of rings. The lubrication of the compressor of a car air conditioner is generally performed by circulating the refrigerant gas containing oil in the sliding portions of the compressor. Therefore, the lubricant oil that is supplied to the sliding surfaces of seat rings and follower rings is little and is in gaseous state because it is mixed in the refrigerant gas. Further, since the lubricant oil is contained in refrigerant gas, the sliding surfaces are not supplied with the lubricant oil for several tens of seconds, or several minutes in a delayed case, from the start of the compressor. Therefore, the sliding portions between the above-mentioned seat rings and follower rings are left in a non-lubricated state so that they are worked in the state of solid contact. Such the state is likewise caused to occur when the cooling medium within the cooling system is decreased by the leakage from pipings or when the quantity of cooling medium returned to the compressor is decreased by the function of an evaporation pressure controller that is attached to an evaporator.
As described above, the shaft-sealing sliding members for the compressors of car air conditioners are naturally used under severe conditions. With the decreasing of car weights in recent years, the compressors are made smaller, lighter and highly efficient. Especially, as the effective means for improving the cooling capacities of compressors, the quantity of oil in refrigerant gas has a tendency to be reduced because the quantity of oil in the refrigerant gas is in inverse proportion to the cooling capacity. Furthermore, in recent years, the engine room is often provided with other devices such as an exhaust gas treating device and a fuel economizing device, so that the temperature of the engine room is liable to become high, and as the result, the use conditions of shaft-sealing sliding members become more strict.
In the conventional art, there have been employed thermal compression molding products as the shaft-sealing sliding members of this kind which are made of the mixture of the simple graphite powder, rubber or synthetic resin binder and low friction fillers such as lead, lead oxide, molybdenum disulfide, iron oxide red, sericite and zinc oxide powder. However, these conventional ones have not been satisfactory to the above-described severe operation conditions.
That is, the conventional shaft-sealing sliding members give good results in the initial stages of sliding work by the addition of the above low friction fillers, however, when they are used for a long time, the initial sliding surfaces (having the roughness which meets with the requirement of sealing character) are changed into mirror surfaces or rough surfaces according to the kind of used filler, especially this is caused by the lack of lubricant oil. When the sliding surface becomes a mirror surface, there will occur no problem if the supply of lubricant oil is sufficient. However, if the lubricant oil is insufficient like the case of the compressor of a car air conditioner, the sliding becomes the solid contact sliding to increase the sliding area. Therefore, the frictional resistance becomes large and the abnormal wearing and seizure are caused to occur. On the other hand, when the sliding surface becomes rough, if the degree of roughening is not excessive, there is no problem in view of the sliding characteristics. However, when viewed from the point of sealing, the leakage is caused to occur in proportion to the degree of roughening.
With regard to the shaft-sealing sliding members for the compressors of car air conditioners, not only the good sliding property but also the sealing property are generally required as described in the foregoing. That is, the sliding surface of the sealing member is generally finished so as to have a suitable roughness (not more than 1 micron) which is akin to a mirror surface. However, the surface should have the sliding characteristic to maintain the state of finished surface.